This invention relates to a light exposure timing and shutter mechanism and, more particularly, to such a mechanism (which includes a disc or a disc-type light shutter, or the equivalent) that can be utilized to control light exposures with a high degree of precision, whereby a wide range of exposure durations can be attained.
Various configurations of the disc or disc-type shutter, such as cones and drums, and the like have been used as light shutters. The disc or disc-type shutter (hereinafter referred to generically and collectively as "disc-type") in its most simple form comprises an opaque disc fitted to (i.e., mounted on) a rotating shaft. An open sector in the disc, when aligned with another aperture (i.e., such as a stationary one), allows light to pass. If the disc is rotated at constant speed, as by a synchronous motor, each time that the open section of the disc passes the stationary aperture, light will be transmitted through the aperture and through the open sector of the shutter for a given duration of time, and that time duration will be a constant for every revolution. This is a very useful type of precision shutter for certain applications. However, for any given rotational speed and for a given stationary aperture size, there are limitations to the exposure durations that the disc can produce. Obviously, the sector cut from the disc cannot become so large that an insufficient opaque sector of the disc remains to close the light path and terminate the exposure. The limitations at the other end (i.e., the short end) of the exposure scale are not so obvious, but they are no less real. Achievable shutter efficiency, and manufacturing tolerances, are two examples.
We have invented a precision light exposure timing and shutter mechanism which, unlike the prior art, can be used to extend the exposure duration range almost indefinitely. We have, thereby, made a significant advance in the state-of-the-art. In addition, our inventive mechanism, also unlike the prior art, obviates the need for critical timing.